Ramesh C. Patel

Adsorption of nicotinic, picolinic, and dipicolinic acids on monodispersed sols of α-Fe2O3 and Cr(OH)3☆

Abstract The adsorption of nicotinic, picolinic, and dipicolinic acids on α-Fe 2 O 3 and Cr(OH) 3 sols consisting of spherical particles of narrow size distributions was measured at solute concentrations up to 4 × 10 −4 mole dm −3 and over a range of pH values at 25°C. The ionic strength was adjusted to 0.05 mole dm −3 with NaClO 4 . The large uptake by Cr(OH) 3 reflected its amorphous structure. Adsorption on the crystalline α-Fe 2 O 3 was more rapid and confined to the external surface of the particles. On both colloids nicotinic acid adsorption was negligible, whereas the uptake of dipicolinic acid approached saturation at the highest concentrations used. Picolinic acid showed intermediate behavior. Adsorption is postulated to involve the use of Lewis acid sites provided by incompletely coordinated metal ions on the surface. Dipicolinic acid also caused slow dissolution of α-Fe 2 O 3 at low pH. The results can be qualitatively interpreted in terms of the complexing power and the acid dissociation constants of the solutes, and the surface acidity of the solids.

Interactions of amino acids with hydrous metal oxides: I. Chromium hydroxide-d-aspartic acid system

Abstract The sorption of aspartic acid on a monodispersed chromium hydroxide sol consisting of uniform spherical particles was studied as a function of pH, temperature, and the amino acid concentration. The uptake of aspartic acid is strongly dependent on pH and shows maximum sorption at pH ∼ 5–6. The amounts adsorbed increase with increasing concentration of the amino acid and no saturation could be achieved. Furthermore, considerably larger amounts were sorbed at 90 than at 25°C. These results indicate that aspartic acid is absorbed in the particles, most likely as a consequence of chelation to chromium ions. No adsorption of tryptophan could be detected on the same colloidal particles. The difference in the behavior of aspartic acid and tryptophan is discussed.

Thermodynamics and kinetics of complexation of iron(III) ion by picolinic and dipicolinic acids

Abstract The complexation reactions of iron(III) with 2-pyridine carboxylic acia (picolinic acid) and 2,6-pyridine dicarboxylic acid (dipicolinic acid) in aqueous solutions have been studied by spectrophotometric and stopped flow techniques. Equilibrium constants were determined for the 1 : 1 complexes at temperatures between 25 and 80°C. The values obtained are: Picolinic Acid (HL): Fe3++ H2L+⇌ FeHL3++H+(K1 = 2.8,ΔH = 2 kcal mole−1 at 25°C, μ = 2.67 M) Dipicolinic Acid (H2D): Fe3++H2D⇌ FeD++2H+(K1K1A= 227 M, ΔH = 3.4 kcal mole−1 at 25°C,μ = 1.0 M). The rate constants for the formation of these complexes are also given. The results are used to evaluate the effects of these two acids upon the rate of dissolution of iron(III) from its oxides.

Physicomechanical properties of epoxidized composite materials from industrial wastes

Abstract Four light-weight engineering construction materials from industrial wastes such as saw-dust, fly ash, cinder and coke were investigated. Various physicomechanical properties of these materials were studied. These inexpensive materials which have better properties than ordinary cement concrete may be of immense use in building technology. Furthermore, reuse of such waste materials may help to alleviate the present-day environmental pollution problems.

Temperature dependences of the formation constants of the cobalt(II) acetate complexes

Abstract The formation constant for the 1:1 complex between Co(II) and acetate ions (CoAc+) has been determined over the temperature range 25–75°C, both by spectrophotometry and by potentiometric titration. At an ionic strength of 1.0 M a near zero enthalpy of formation ws found. A spectrophotometer cell suitable for use up to ∼250°C is described and spectra of Co(II) acetate solutions are presented at temperatures up to 200°C. At elevated temperatures a tetrahedral species having the composition CoAc2 is formed. The role of the complexation of Co(II) by acetate in the precipitation of Co3O4 from solutions of Co(II) acetate is briefly discussed.

A thermodynamic study of magnesium(II) interactions with mono- and dinucleotides☆

Abstract The equilibrium constants for the interaction between magnesium(II) and a number of mono- and dinucleotides (AMP, TMP, GMP, CMP, d-ApA, d-TpT, d-GpG, d-CpC, d-pTpT) have been determined accurately at 25.0 °C and an ionic strength of 0.2 M by a computerized, multiparamagnetic curve fitting analysis of pH titration curves. The data are consistent with inner sphere binding of magnesium(II) with the phosphate group. The presence of an additional base in those dinucleotides without a terminal phosphate causes a decrease in the magnesium(II) association constant.

Simultaneous determination of kinetic and thermodynamic parameters from fast-reaction kinetic measurements

A combined stopped-flow temperature-jump apparatus interfaced with a dedicated microcomputer has been used to study the complexation reaction of iron(III) with thiocyanate in aqueous solution. Kinetic rate-constants (k(f) = 143 l.mole(-1) .sec(-1) from T-jump, k(f) = 150 l.mole(-1) .sec(-1) from stopped flow), equilibrium constants (K = 143 from T-jump, K = 150 from stopped flow) and the thermodynamic enthalpy change (DeltaH(c) = -6.7 kJ/mole) could be independently determined from the simultaneous application of the two techniques.

Ultracentrifuge as a Versatile Tool to Study Preferential Interaction of Polymers in Mixed Solvents

Abstract Over the past five decades the analytical ultracentrifuge has been a versatile tool in the study of macromolecules and colloidal particles. Several textbooks [1–4] and review articles [5–10] deal with experimental techniques and theories for complete characterization of macromolecular species. However, the first published articles on the analytical ultracentrifuge dealt with the analysis of particle size distributions in suspensions of inorganic colloids. The emphasis has now shifted to organic polymers following the discovery that a large number of such polymers exist in nature. Before the development of the ultracentrifuge, the existence of such giant molecules was not recognized; the molecular kinetic units of proteins and of high organic polymers in solution were simply thought of as clusters of much smaller molecules, forming particles of undefined mass. Beginning with the elegant investigations of Svedberg [11, 12] on ultracentrifugation, such substances were revealed to be macromolecules, ...

Noise reduction in relaxation kinetic experiments.

The use of high-speed digital data-acquisition devices makes it possible to obtain a large number of points (>4000) for a single experiment during a short time interval. A suitable numerical treatment capable of reducing the periodic and random noise in relaxation-curves and of providing relaxation times and amplitudes of high accuracy is presented.

Microcells for fluorescence and spectrophotometric studies of biologically active compounds

Abstract A spectrophotometric cell requiring 20 μl of sample solution and usable at elevated temperatures (∼80°C) is described. Details of fluorescence microcells with capacities ranging from 8 to 80 μl are provided. The external dimensions of both cells are maintained for use in commercially available instruments. Sample solutions come in contact only with chemically inert Teflon, Viton, or quartz. The utility of these cells in spectral measurements involving scarcely available biologically active oligonucleotides such as the lac operator core, the recognition site of BamHI restriction endonuclease, as well as the peptide hormone somatostatin, is demonstrated. In combination with photon counting techniques, it is possible to undertake experiments with picogram quantities of material.